Method of preparing cellulose acetates



Patented July 17, I934 METHOD OFPREPARING CELLULOSE .AGETATI JS.

Van L. Bohnson, 'Waynesboro, .VaL', ,assignor (to I "Du Pont Rayon Company, New york, N.Y., a 1

corporation of Delaware 1N0 Drawing;

'APPl a enKwember-M, 1932, .7 Serial No.

d-claims. (or. 250-401 This invention relates .tothe .productionbf artificial thread .:formed of .a plurality of cellulose acetates which, uponsubsequent treatment with 'hot water or hot soap solutions, such as .at ornear the boiling point thereof, or steam, loses a considerable portion of its luster and assumes a dull or mat appearance. More particularly, the instant invention :relates :to a process of preparing a mixture of cellulose acetates to be used in the production of artificial thread .of the type immediately aforementioned.

I he Bohnson .and Swezey application, Serial No. 624,897, filed July 26, 1932, discloses spinning a solution containing .a plurality of celluc -lose acetates having different characteristics, such as different acetyl values '(calculated as acetic acid for the purpose of producing a .thread which,upon-treatment-with steam or hot liquids, such as water orsoapsolutions at ornear the boiling point thereof, will be :readily delustered. According to the Bohnson and Swezey application, the desired results mayibe secured if the thread is .formed of'aplurality of :celluloseacetates, such as 5'0%95%"by weightof a celluloseacetate'having an a'cetyl value, calculatedas acetic acid, of 54%-'56,%, and 5%5.0%'

by weight-ofa cellulose-acetate having an acetyl value, calculated as acetic acid-,=of:43"%-53%. =In the preferred embodiment, Bohnson and Swezey contemplate athread composed of- 90%- 96% of a cellulose acetate having an'acetyl value calcu la-ted-asacetic acid-of 5'4'%-55%; -and-4%'- 10% of a cellulose acetate having an acetyl value, calculated-as acetic acid, of 45 %-47% I have found that I can produce a thread having the characteristics previously mentioned by spinning, and preferably by the dry spinning process, a solution containing a mixture of acetates having the desired average acetyl value by hydrolyzing a solution containing a plurality of acetates having difierent acetyl values until the desired average acetyl value of the mixture is secured.

It is, therefore, an object of this invention to provide a method of preparing a mixture of a plurality of cellulose acetates, each of said acetates having different characteristics, which comprises hydrolyzing a solution containing a plurality of acetates having different acetyl -values until the desired average acetyl value of the mixture is obtained.

A specific object of this invention is to provide a method of preparing a mixture of a plurality of cellulose acetates which comprises in- :corpcrat -ns .in a solution onta nms p ma y aceta,te ,.;for examplethe solution secured at the end .Of the usual acetylation pf .cellulose with ac ti :acid, acetic anhydrid a eatalr a cellulose acetate havin an acety value, ,calcu lated as ac t a id, difi e fr m t at c th prim -y acetat and such as a ce los zacetatezlmvmg a e yl v lue. cal u a d .as acetic acid. aQf 54% 5 .%.,-end then hydro yz n the mixture of said acetates until the average acetyl value, calculated :a ac tic acid. of the mixture of the wacetates, :18 approximately Qther objects will appear -,fr omthe fol1owing .descriptionandappendedclaims.

in accordance "with the principles .of th instant invention, .eellulosem acetylated-in the usual manner with for ex mple acetic aci lacetiezanhrdrid and-a aaly t,- as s iphuric acid, until the pri,mary acetate is pro,- tduced. At theendmi the acetylation operation, the primary cellulose acetate is .dissolved ,in the aceticacid, ,andto thissolution there is added a predeterminedquantity of ,a cellulose 'acetate which ,is' characterized .by an acetyl value difierehtfrom-that of the 'primary acetate. After thoroughly mixing, the mixture isflhydrolyzed as'is well known in the art until the desired average acetyl-content of the mixture of the acetates is-secured. Theresulting mixed acetate in the ;mass are then" precipitated with water, washed, :and dried in the: :usual manner.

The product of .;theiforegoi-ng procedure is a homogeneous and uniform mixture of acetates and forms, when dissolved in appropriate solvents, a spinning solution which uponbeing spun, for example by the dry spinning process, produces a thread which upon treatment with steam or hot liquids, such as water or soap solutions, at or near the boiling point thereof, 56 will be readily delustered.

It is obvious that the quantity of cellulose acetate added to the solution containing the primary acetate depends partly upon the relative quantities of the diflerent cellulose acetates desired in the mixture. Likewise, the acetyl value, calculated as acetic acid, of the cellulose acetate added to the solution of the primary acetate depends partly on the average acetyl mixture desired in the final product. Satisfactory results have been secured when 5%-20% of cellulose acetate having an acetyl value, calculated as acetic acid, of approximately 54%55% was added to the primary acetate solution and the hydrolysis continued until the average acetyl value, calculated as acetic acid, was approximately 53%-54=%.

In the preferred embodiment of the invention, the cellulose acetate which is added to the primary acetate solution is preferably soluble therein. In one embodiment of the invention, the added cellulose acetate may be in the finely divided state. Alternatively, the added acetate may be previously dissolved in a suitable sol-- vent, such as acetic acid, and then added to the primary acetate solution.

In order to explain more fully the principles of this invention, the following illustrative example is set forth. It is, of course, to be understood that the invention is not restricted thereto but is merely illustrative.

Eccample.To 21.6 parts of cellulose acetate in solution in acetic acid at the end of the primary acetylation there is added 2.4 parts of cellulose acetate having an acetyl value, calculated as acetic acid, of 54%-55%, either in the form of finely ground material or in solution in acetic acid. After thoroughly mixing the same, the mass is subjected to the well-known hydrolysis operation which is continued until the average acetyl values of the mixture of cellulose acetates is approximately 53 %-54%. At this time, the resulting mixed acetate is precipitated With water, washed, and dried in the usual manner.

The resulting product is a heterogeneous mixture of the plurality of acetates. A predetermined quantity of this mixture of acetates is then dissolved in appropriate solvents, such as mu, acetone, or acetone and alcohol, to produce a spinning solution of suitable concentration, such as, for example, one containing 20%-30% of said mixture of acetate. Upon spinning such a solution by the dry spinning process there is v obtained a thread which is characterized by a normal luster. 'The thread either prior to or subsequent to weaving or knitting into cloth, when subjected to, for example, a boiling 2% soap solution for approximately 1 hour, acquires or assumes a dull or mat appearance.

Though the invention has been particularly described in connection with a mixture of two acetates of different characteristics, it is to be understood that the invention is not restricted thereto, since it is obvious that more than two acetates may be employed with equal success. Also, the method herein described is equally applicable to the production of mixed acetates for any purpose.

Since it is obvious that various changes and modifications may be made in the above description without departing from the nature or spirit thereof, this invention is not restricted thereto except as set forth in the appended claims.

I claim:

1. A method of preparing a mixture of a plurality of cellulose acetates, each of said acetates having different characteristics, which comprises acetylating cellulose until a primary cellulose acetate is produced, incorporating in the primary acetate solution a cellulose acetate having an acetyl value different than said primary acetate, and hydrolyzing the acetates until the desired average acetyl value of the mixture of acetates is secured.

2. A method of preparing a mixture of a plurality of cellulose acetates, each of said acetates having different characteristics, which comprises acetylating cellulose until a primary acetate is secured, incorporating a cellulose acetate having an acetyl value, calculated as acetic acid, of approximately 54%-55% in the solution containing said primary acetate, and hydrolyzing the acetates until the average acetyl value, calculated as acetic acid, of the mixture of acetates is approximately 53%-54%.

, 8. A method of preparing a mixture of a plurality of cellulose acetates, each of said acetates having different characteristics, which comprises acetylating cellulose until a primary acetate is secured, incorporating 5%-20% of a cellulose acetate having an acetyl value, calculated as acetic acid, of approximately 54%-55% in the solution containing said primary acetate, and hydrolyzing the acetates until the average acetyl value, calculated as acetic acid, of the mixture of acetates is approximately 53%-54%.

4-. A method of preparing a mixture of a plurality of cellulose acetates, each of said acetates having different characteristics, which comprises acetylating cellulose until a primary acetate is secured, incorporating a cellulose acetate having an acetyl value, calculated as acetic acid, of approximately 54%-55% in the solution containingsaid primary acetate and in such an amount as to constitute 10% of the combined acetates, and hydrolyzing the acetates until the I average acetyl value, calculated as acetic acid, of the mixture of, acetates is approximately 53 %-54%. v

VAN L. BOHNSON. 

